In the art of container manufacture, the term "container finish" generally refers to that portion of the container that defines the container mouth. In a bottle, for example, the finish includes that portion of the container neck having threads and/or shoulders for receiving the container cap, as well as the upper surface of the neck surrounding the container mouth against which the cap seats. It is important that the container finish be properly manufactured and possess desired external geometric characteristics so that a cap may be affixed thereto to seal the container against leakage and escape of carbonation during handling and storage.
U.S. Pat. No. 4,701,612, assigned to the assignee hereof, discloses a method and apparatus for inspecting the finish of transparent containers, particularly glass containers, which include facility for directing diffused light energy laterally through the container finish as the container is rotated about its central axis. A camera includes a plurality of light sensitive elements or pixels disposed in a linear array angulated with respect to the container axis and coplanar therewith to view the external and internal wall surfaces, the latter through the open container mouth. Individual elements of the camera linear array are sampled by an information processor at increments of container rotation, and corresponding data indicative of light intensity at each element is stored in an array memory as a combined function of element number and scan increment. Such data is compared following completion of container rotation to standard data indicative of an acceptable container finish, and a reject signal is generated if such comparison exceeds an operator-adjustable threshold.
U.S. Pat. No. 4,958,223, also assigned to the assignee hereof, discloses a method and apparatus for inspecting the finish of a container as the container is held and rotated about its central axis. A light source is positioned to direct diffused light energy onto the container finish, and a camera is positioned across the axis of the container from the light source. The camera comprises a matrix array sensor positioned with respect to the camera focusing elements to receive an image of the container finish as illuminated by the light source. Information processing electronics are coupled to the camera array for indicating optical characteristics of the container finish as differing functions of light intensity incident on the matrix elements for detecting structural commercial variations or geometric parameters of the container finish.
Although the systems so disclosed in the noted patents represent significant advances as compared with previous finish inspection techniques, further improvements remain desirable. For example, in applications in which it is specifically desired to measure external dimensional parameters of the container finish, as opposed for example to internal structural variations in the container finish area, it is highly desirable to develop a sharp image of the container profile--i.e., an image in which transition at the profile edges is characterized by high contrast and sharp transition between light and dark. A general object of the present invention is to provide a system and method that is characterized by such a sharp transition at the profile image edges, and thus are adapted for obtaining improved and enhanced measurement accuracy of finish profile dimensional parameter measurements.
Apparatus for inspecting external dimensional parameters of a container finish in accordance with the present invention includes a light source for directing light energy onto the finish of the container and a matrix array sensor disposed to receive an image of the container finish illuminated by the light source. A telecentric lens and camera lens combination is positioned to focus onto the matrix array sensor an image of the container finish profile formed by light energy traveling parallel to the telecentric lens axis, such that the finish profile appears as a dark image against a light background at the sensor. The matrix array sensor is scanned, preferably at increments of container rotation, to develop multiple electronic two-dimensional images of the finish profile, each from a different azimuthal position with respect to the finish, from which one or more dimensional parameters are determined. Use of the telecentric lens arrangement effectively to reject light rays that are non-parallel to the optical axis of the lens and camera provides an image of the container finish that is characterized by high contrast between the dark image and the light background, and a sharp non-ambiguous transition at the profile edges.